Messages in this thread Patch in this message | | | From | "Paul E. McKenney" <> | Subject | [PATCH tip/core/rcu 3/9] rcu: Create call_rcu_tasks() kthread at boot time | Date | Wed, 4 Oct 2017 14:29:29 -0700 |
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Currently the call_rcu_tasks() kthread is created upon first invocation of call_rcu_tasks(). This has the advantage of avoiding creation if there are never any invocations of call_rcu_tasks() and of synchronize_rcu_tasks(), but it requires an unreliable heuristic to determine when it is safe to create the kthread. For example, it is not safe to create the kthread when call_rcu_tasks() is invoked with a spinlock held, but there is no good way to detect this in !PREEMPT kernels.
This commit therefore creates this kthread unconditionally at core_initcall() time. If you don't want this kthread created, then build with CONFIG_TASKS_RCU=n.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- kernel/rcu/update.c | 24 +++++------------------- 1 file changed, 5 insertions(+), 19 deletions(-)
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 9e599fcdd7bf..ed5922857384 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -585,7 +585,6 @@ DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu); static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT; module_param(rcu_task_stall_timeout, int, 0644); -static void rcu_spawn_tasks_kthread(void); static struct task_struct *rcu_tasks_kthread_ptr; /** @@ -610,7 +609,6 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) { unsigned long flags; bool needwake; - bool havetask = READ_ONCE(rcu_tasks_kthread_ptr); rhp->next = NULL; rhp->func = func; @@ -620,11 +618,8 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) rcu_tasks_cbs_tail = &rhp->next; raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); /* We can't create the thread unless interrupts are enabled. */ - if ((needwake && havetask) || - (!havetask && !irqs_disabled_flags(flags))) { - rcu_spawn_tasks_kthread(); + if (needwake && READ_ONCE(rcu_tasks_kthread_ptr)) wake_up(&rcu_tasks_cbs_wq); - } } EXPORT_SYMBOL_GPL(call_rcu_tasks); @@ -863,27 +858,18 @@ static int __noreturn rcu_tasks_kthread(void *arg) } } -/* Spawn rcu_tasks_kthread() at first call to call_rcu_tasks(). */ -static void rcu_spawn_tasks_kthread(void) +/* Spawn rcu_tasks_kthread() at core_initcall() time. */ +static int __init rcu_spawn_tasks_kthread(void) { - static DEFINE_MUTEX(rcu_tasks_kthread_mutex); struct task_struct *t; - if (READ_ONCE(rcu_tasks_kthread_ptr)) { - smp_mb(); /* Ensure caller sees full kthread. */ - return; - } - mutex_lock(&rcu_tasks_kthread_mutex); - if (rcu_tasks_kthread_ptr) { - mutex_unlock(&rcu_tasks_kthread_mutex); - return; - } t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread"); BUG_ON(IS_ERR(t)); smp_mb(); /* Ensure others see full kthread. */ WRITE_ONCE(rcu_tasks_kthread_ptr, t); - mutex_unlock(&rcu_tasks_kthread_mutex); + return 0; } +core_initcall(rcu_spawn_tasks_kthread); /* Do the srcu_read_lock() for the above synchronize_srcu(). */ void exit_tasks_rcu_start(void) -- 2.5.2
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